I find it makes far more sense with Cobb waking up on the plane and living his life in the real world. If you make it so that it was "all a dream" It kinda negates all the drama in the film if there were never consequences for any of the actions. Besides, Cobb was on the very precipice of succeeding in his heist when he was talking to his wife in Limbo which took on the pretense of a 4th dream which Leo created out of his memories of the world he and his wife created. This is why Ellen Page's character couldnt change the world in that 4th dream, and neither could Cobb - his wife was dead, so he was only creating half the image so to speak, which is why it was collapsing.
Plus, when he is talking to his wife, he constantly reiterates about going home to his kids whom he has a real chance of seeing, the ones she "left" in his own words, I don't think he's ever really convinced by the memory, he just stays too long in the 4th dream, which then collapses into limbo where he meets Ken Watanabe's character as an old man. He then reminds him of what happened just so he can go back to his kids. If the guy has gone through all this, and is in limbo and STILL wants to rescue the man who can get him off the hook just so he can go back to his kids, I don't think he's gonna settle for a dream, whether he knows it or not.
By the end of "limbo", Cillian Murphy and Ellen page had "shocked" themselves out of the 4th collapsing dream by falling, When they returned to the 3rd snow dream, they were all then shocked out of that by the Elevator falling, and in that 2nd dream, they were shocked out of it by the Car hitting the river. The two who were in Limbo remained there until the sedative wore off, which for those in the first dream was a matter of moments, whereas to Cobb and Watanabe was years, hence the air of madness to their meeting in the dining hall at the end.
Again, I can't see how a man who had clung onto this belief that he could see his children again for real would go through all these levels of insanity inducing time and still cling onto that belief until the very end until the sedative wore off and they were awoken from limbo by the gun that Watanabe shot himself with, and when he dissappeared Cobb probably realised he could leave and then shot himself to wake up.
They then landed at LAX (Not in Purgatory - fuck you LOST) and then went their seperate ways. He goes home, places the totem on the table, spins it and then Cobb sees his children again for the first time since his wife died, ignoring the totem.
Again, I took the spinning totem as a metaphor for Cobbs dream, where he would see them again. He was now living that dream, and the totem was a visual cue as to the characters progression. We saw it wobble quite violently, unlike the shots of it in the dream world and the shot cut before we saw it fall. Once again, if it had last a second longer, we'd have seen that totem fall, but Christopher Nolan just loves to leave the audience hanging with questions, and that's his prerogative.